1. Field of the Invention
The present invention relates to a method of producing a substrate for a recording head wherein an electro-thermal converting element and a recording function element are formed on a supporting member and to a method of producing a recording head employing the substrate for a recording head. Particularly the present invention relates to a method for producing a recording head and a substrate used for the recording head which are utilized in a recording head apparatus for a copying machine, a facsimile, a word processor, an out-put printer of a host computer and an out-put printer for video apparatus.
2. Related Background Art
Conventionally, a recording head comprises an electro-thermal converting element formed on a supporting member of single-crystal silicon and a driving functional element for driving the electro-thermal converting element such as a transistor array and so forth disposed out of the supporting member, wherein connecting of the electro-thermal converting element and the transistor array is carried out by a flexible wire or wire bonding.
An ink discharging recording head having an electro-thermal converting element and a driving functional element formed on the same supporting member for simplifying the structure of the aforementioned head constitution and reducing a defect generated in the manufacturing process and also for uniforming and improving the reproducibility of the characteristics of each element, which is proposed in Japanese Patent Application Laid-Open No. 57-72867 (corresponding to U.S. Pat. No. 4,429,321), is known.
FIG. 25 is a cross-sectional view of a part of a substrate for a recording head according to the aforementioned constitution. Numeral 901 is a semiconductor supporting member composed of a single-crystal silicon. 904 is an epitaxial region of n-type semiconductor and 911 is an ohmic contact region of a n-type semiconductor with high concentration of impurity. 905 is a base region of a p-type semiconductor, 910 is an emitter region of a n-type semiconductor with high concentration of impurity and a bipolar transistor. 930 is composed thereby. 921 is a heat accumulating layer and 922 is an oxidized silicon layer as an interlaminar insulating layer. 923 is a heat-generating resistance layer, 924 is a wiring electrode of aluminum (Al) and 925 is an oxidized silicon layer as a protecting layer and a substrate 900 for a recording head is composed of these. Here, 920 acts as a heat generating portion. A recording head is completed by forming a ceiling plate and liquid pathes on the substrate 900.
Thus the bipolar transistor 930 has a n-p-n transistor structure comprising two high concentration n-type collector regions 911 formed on a n-type collector buried region 902 and the p-type silicon supporting member 901 through the n-type collector buried region 102, two high concentration p-type base region 908 formed inside of the high concentration n-type collector 911 on the n-type collector buried region 902 and through a p-type base buried region 905, and the high concentration n-type emitter region 910 formed between a high concentration p-type base regions 908 through the p-type base region 905 and on the n-type collector buried region. The bipolar transistor 930 acts as a diode by connecting the high concentration n-type collector region 911 and the high concentration p-type base region 908 with a collector base common electrode 912. Further a p-type isolation buried region 903 as an element separating region, a p-type isolation region 906 and a high concentration p-type isolation region 909 are formed successively. A heat generating layer 923 is formed on the p-type silicon supporting member 901 through a n-type epitaxial region 904, a heat accumulating layer 921 and an interlaminar layer 922. By cutting a wiring electrode 924 formed on the heat resistance layer 923, a heat generating member 920 is formed. Further the top surface of the supporting member 900 for an ink discharging recording head is covered by a first protective film 925 and the first protective film 925 covering the range from the high concentration n-type emitter region 910 of the bipolar transistor 930 to the heat generating member 920 is covered further by a second protective film 926. An ink jet recording head substrate 900 having a structure as above mentioned can be manufactured by a process for a semiconductor utilizing a known photolithographic technique.
Although the aforementioned structure shows improved performances, in order to satisfy requirements to be demanded strongly for a recording apparatus such as a high speed driving, energy saving, high density integration, cost reduction and higher reliability, still further developments are necessary.
FIGS. 26A to 26E are illustrative views of processes of etching of a material layer 824 for wiring electrode on the heat generating member 920. A material layer 824 for a wiring electrode (for example, A1) is formed entirely on the heat generating resistance layer 923, a photoresist for masking 1000 is coated entirely on the material layer 824. After exposing the photoresist 1000 by light with a mask and developing to remove the photoresist corresponding to the portion to be etched of the material layer 824 for the wiring electrode (FIG. 26A). Then the material layer 824 for the electrode is etched by an etching liquid, and at the portion of material layer for the electrode where the photoresist for masking 1000 is removed an electrode for wiring 924 is etched slowly and successively is formed by cutting the material layer for wiring 824 (FIGS. 26B to 26D). The remained photoresist for masking 1000 is removed after forming the electrode 924 (FIG. 26E).
However, in the aforementioned substrate 900 for an ink jet recording head, since the edge part 924-1 of the wiring electrode 924 on the heat generating portion 920 may tend to form near perpendicular shape as shown in FIG. 26E, the problem described below is taken place.
(1) When an electric current is sent from the high concentration n-type emitter portion 910 to the wiring electrode 924, the current of electricity is concentrated in the lower part of 924-1 as shown by arrows in FIG. 27. That is, according to an experimental result the current density of edge part 924-1 reaches to 8.2.times.10.sup.7 A/cm.sup.2 and it is outstandingly large value compared with 1.7.times.10.sup.6 A/cm.sup.2 of that in the wiring electrode 924 and 1.03.times.10.sup.7 A/cm.sup.2 of that of the central part of the heat generating resistance layer 923. It has been considered that the concentration of the current in the lower part of the edge part 924-1 results breaking of a part of the heat generating resistance layer 923 and may deteriorates the life time of a liquid discharging recording head.
In general, in a conventional substrate for recording head, when the wiring material such as Al, etc. is removed by a wetting treatment, since the Al is removed isotropically the material may be mostly formed to a shape of electric resistance member namely a heat generating member as shown in FIG. 27. While if wiring electrode 908 is removed by a dry etching method such as RIE method as so on, the edge part 910 as the connecting portion of Al will tend to shape more perpendicularly. When thus shaped electric-thermal converting element is driven, the current passes by applying with electric voltage as an arrows as shown in FIG. 27. As a result, the concentration of the current density in edge part 907A or 907B of the heat generating resistance layer may break a part of the heat generating resistance layer 907.
(2) For improvement the coverage of the heat generating portion 920, since a thickness of a first protective film 925 is necessary to provide for example, about 1.0 .mu.m, and the protective layer 925 acts a heat resistance layer against to heat conduction of the heat energy from the heat generating portion 920 to a liquid (ink) to be discharged, the driving power for the heat resistance layer 923 has to be large and a deterioration of a frequency characteristics caused by the delay of heat conduction may occur and as a result, this is one of factors to prevent from the saving consumption of energy and the developing higher performance apparatus.
In more detail, there is necessity to make the thickness of the interlaminar layer 906 and the protective film 909 to be about 1.25 .mu.m and about 1.0 .mu.m respectively for well step-covering because the edge part 910 for the connection surface of the electrode and the each wall is stood perpendicularly.
The thickness as about 1.25 .mu.m, relatively thick for the interlaminar layer, deteriorates remarkably the through put of an apparatus and is a bottle necking for the cost reduction.
The too much thickness of about 1.0 .mu.m as a protective film acts as a heat resistance against the heat conduction of the heat generated at the heat generating portion 940 to an ink, therefore the driving power for the resistance member has to be large and a deterioration of a frequency characteristics caused by the delay of heat conduction may occur.
The existing of the relatively thick film as insulating film has prohibit from making higher the performance of a conventional heat and saving electricity consumption.
Furthermore, conventionally an interlaminar film 906 and a protective film 909 and etc. have formed by a method such as a normal pressure CVD or PCVD utilizing PSG (phosphoric silicate glass: SiO.sub.2 film containing phosphorus (P); formed from PH.sub.3 +SiH.sub.4 +O.sub.2), BPSG (boron phosphoric silicate glass: SiO.sub.2 film containing boron (B) and phosphorus (P); formed from B.sub.2 H.sub.6 +PH.sub.3 +SiH.sub.4 +O.sub.2), SiO, SiO.sub.2, SiON and SiN at 0.degree.-450.degree. C. At this temperature range, on a wiring, an electrode, etc. made of Al, etc., when the film is deposited (grown) by CVD method, a rising made of Al and etc., named hillrock, (often the height and diameter are about 2 .mu.m) is generated and grown, finally the irregularity of the hillrock 204 may make short-circuit, for example, between the emitter electrode 201 and the wiring electrode 202 or between these wirings and a protective film made of Ta (for example a protective film 926 shown in FIG. 25) and may result a fault of the action and lowers the efficiency of the production.